U3 KA4a - Cells Of The Nervous System

Question 1

What is the Cell body of a Nerve cell?

Answer 1

The cell body contains the nucleus and most of the cytoplasm. It is the control centre of cell metabolism

Question 2

What is the axon of a Nerve cell?

Answer 2

An axon is a single nerve fibre that carries nerve impulses away from a cell body.

Question 3

What are the dendrites of a Nerve cell?

Answer 3

Dendrites are nerve fibres which receive nerve impulses and pass them towards a cell body.

Question 4

What is the path of a nerve impulse in a nerve cell?

Answer 4

Dendrites -> Cell Body -> Axon

Question 5

What are the 3 types of neurons

Answer 5

Sensory, Interneurons and motor neurons

Question 6

Describe the role of Sensory Neurones

Answer 6

Carry impulses into the Central Nervous System (CNS) from sense organs

Question 7

Describe the role of Interneurones

Answer 7

Found in the CNS where they connect with other neurons

Question 8

Describe the role of Motor Neurones

Answer 8

Carry impulses out from the CNS to effectors such as muscles and glands

Question 9

What is the Myelin sheath?

Answer 9

Myelin is the fatty tissue that insulates an axon

Question 10

What does the Myelin Sheath do?

Answer 10

The presence of myelin greatly increases the speed at which impulses can be transmitted

Question 11

What is Myelination?

Answer 11

Myelination is the name given to the process of myelin developing round axon fibres

Question 12

When is Myelination complete?

Answer 12

Myelination increases from birth to Adolesence

Question 13

Certain diseases damage or destroy the myelin sheath causing…

Answer 13

a loss of co-ordination (due to slower impulses).

Question 14

State the roles of Glial Cells​

Answer 14

Some types of glial cells are responsible for myelination of neurons. ​

Some lay down tightly packed layers of plasma membrane around an axon. ​

Other glial cells act as a support for neurons. e.g. Producing chemicals the neurons need to function.

Question 15

What is a Synapse?

Answer 15

A synapse is the tiny gap between an axon ending of one neuron and the dendrite of the next neuron in the pathway

Question 16

What is the nerve cell before the synaptic cleft Called?

Answer 16

The presynaptic neuron

Question 17

What is the nerve cell after the synaptic cleft Called?

Answer 17

Postsynaptic neuron

Question 18

Describe the transmittion of a nerve impulse across the synaptic cleft

Answer 18

Neurotransmitters are stored in vesicles at each end of the presynaptic neuron (the presynaptic terminal). ​

When a nerve impulse arrives, the vesicles moves to fuse with the membrane of the neuron and release the neurotransmitter into the synaptic cleft ​

The neurotransmitters then diffuse across the synaptic cleft and bind to receptors on the postsynaptic membrane

Question 19

What are Neurotransmitters stored in?

Answer 19

vesicles

Question 20

Describe the direction of travel for neurotransmitters

Answer 20

Nerve impulses can only travel in one direction.

Question 21

Why are neurotransmitters quickly removed from the synaptic cleft between impulses?

Answer 21

To prevent continuous stimulation of postsynaptic neurones

Question 22

State 2 ways in which Neurotransmitters can be remover from the synaptic cleft

Answer 22

1. Re-uptake ​
2. Enzyme degradation

Question 23

Describe the Re-uptake of Neurotransmitters

Answer 23

The neurotransmitter is reabsorbed directly back into the presynaptic membrane that secreted it. ​

It is then stored again in vesicles ready for use for future impulses

Question 24

Describe the Enzyme Degradation at the synaptic cleft

Answer 24

The neurotransmitter is broken down by an enzyme to form non active products. ​

These products are then reabsorbed by the presynaptic neurone and re-synthesised into active neurotransmitter (packaged in vesicles)

Question 25

What are the two types of signals received at the post synaptic neurone?

Answer 25

1. Excitatory
2. Inhibitory

Question 26

Excitatory Signals…

Answer 26

increase impulses sent to effectors

Question 27

Inhibitory Signals

Answer 27

decrease impulses sent to effectors

Question 28

Why may a nerve impulse not be transmitted across the synapse?

Answer 28

Not enough neurotransmitter molecules were released - Threshold was not reached

Question 29

What is summation?

Answer 29

A series of weak stimuli (from neighbouring neurones) combine to trigger enough neurotransmitter to fire an impulse in the post-synaptic neurone